Proposal for PPLN-Based All-Optical NRZ-to-CSRZ, RZ-to-CSRZ, NRZ-DPSK-to-CSRZ-DPSK, and RZ-DPSK-to-CSRZ-DPSK Format Conversions

A simple realization of 40-Gb/s all-optical format conversions from nonreturn-to-zero (NRZ) to carrier-suppressed return-to-zero (CSRZ), from return-to-zero (RZ) to CSRZ, from NRZ differential phase-shift keying (NRZ-DPSK) to CSRZ-DPSK, from RZ-DPSK to CSRZ-DPSK are proposed and numerically demonstrated based on cascaded second-order nonlinearities in a periodically poled lithium niobate waveguide. A carrier-suppressed pump clock is adopted. The spectra, waveforms, eye diagrams, and constellation diagrams are investigated. Multicasting, multichannel, and ultrahigh-speed (160 Gb/s) operations are also numerically demonstrated.